When World War I first broke out, the United States charted a path towards neutrality. Regardless, this did not prevent it from being pulled into the war.
The thing I would suggest to keep in mind is that, while the United States did not enter the war until 1917, the path was being laid well before. In 1915, a German submarine sank the Lusitania, spurring outrage and anti-German sentiment throughout the United States. Consider also the impact of the Zimmermann Telegram and the revelation that Germany was making overtures to draw Mexico into the war (along with its willingness to assist Mexico in acquiring territorial concessions from the United States in the event of victory) should the United States intervene. Meanwhile, be aware that Germany was resuming its use of unrestricted submarine warfare.
Thus, in April, 1917, the US entered the war. Keep in mind the sheer scale of destruction and devastation that World War I visited upon Europe. By this point, both sides were exhausted and near to the point of collapse. Having the United States intervene at such a late stage proved decisive. By the time the war's conclusion, roughly two million American troops had arrived foot in Europe. To this, one might add the role that the American navy played in supporting the British blockade of Germany. Also note the importance of United States economy and the impact of its production capabilities (agricultural, manufacturing, etc).